Method of retreading tire casings



Nov. 25, 1941. P. E. HAWKINSON 21,956

METHOD OF RETREADING TIRE CASINGS Original Filed May 14, 1951 3 Sheets-Sheet l i ii!- Nov. 25, 1941. P. E. HAWKINSON METHOD OF RETREADING TIRE CASINGS Original Filed May 14, 1931 5 Shee1isSheet 2 Nov. 25, 1941. P. E. HAWKINSON METHOD OF RETREADING TIRE CASINGS Original Filed May 14, 1931 3 Sheets-Sheet 3 and 1250]) Reissued Nov. 25, 1941 21,956 METHOD orne'rannnmo rmc casinos Paul E. Hawkinson, Minneapolis,

to Paul E. Hawkinso Minn., a corporation Original No. 1,917,261,

reissue August 15, 1941, Serial 13 Claims. I

My present invention relates to an improved method of retreadlng tire casingssuch as used on motor vehicles, and further to an improved apparatus for use in carrying out the improved method.

An important object of the invention is to provide a simple and highly efficient method of applying new tread to the road engaging crown portions of tire casings to replace that which has been worn off or removed without removing or materially changing the appearance of the original shoulder tread portions or side wall of the tire, thereby saving the original ornamental design of the tires, leaving them readily identifiable as to make, reducing to a minimum the labor required to prepare tires for and to perform a retreading operation and further materially reducing the amount of new material required.

Another important object of this invention is to provide a method whereby tire. casings of varying sizes can be entered into and have new treads formed thereon in a single size annular matrix. Still another object of the invention is the provision of an extremely inexpensive but highly eiiicient apparatus for retreading tires.

Generally stated, the invention relates to a novel method, devices, combinations of devices and arrangement of parts hereinafter described and defined in the claims.

- In the accompanying drawings, which illustrate the invention, like characters indicate like parts throughout the several views.

Referring to the drawings:

Fig. l is a perspective view matrix;

Fig. 2 is a fragmentary perspective view of a worn tire casing, before retreading;

Fig. 3 is a cross-sectional view of the casing after having a new but unformed crown tread applied thereto;

Fig. 4 is a view in side elevation illustrating the casing in a circumferentially contracted condition within the matrix;

Fig. 5 is a fragmentary sectional view taken on the line 5-5 of Fig. 4;

Fig. 6 is a fragmentary sectional view similar to Fig. 5 but illustrating the newly treaded casing circumferentially expanded against matrix and before application of vulcanizing heat;

Fig. 'I is a fragmentary sectional View similar to Fig. 6 but illustrating the retreaded casing as it appears in the matrix after vulcanizing;

Fig. 8 is a fragmentary perspective view of the casing removed from the matrix after completion of the retreadin'g process; and

of an improved n Company,

Minnesota Minn, asslgnor Minneapolis,

dated July 11, 1933, Serial No. 537,324; May 14, 1931. Application for Fig. 9 is diagrammatic view illustrating the customary cord carcass construction of tire cas ings.

The improved matrix is comprised of a continuous, unbroken and non-separable annular section 9 that is substantially straight in axial cross-section and is provided near opposite edges of its inside surface with annular retaining ribs II) and intermediate said retaining ribs with annular tread design-forming ribs II. This matrix is adapted for use with tire casings having a greater normal circumference than that of the inside of said matrix and the casings are entered thereinto in a manner hereinafter described. The annular retaining ribs III are continuous and unbroken but the tread-forming ribs II are formed of circumferentially aligned segments that are spaced apart slightly to form gates I2. Between the several ribs III and II the annular matrix member 9 is provided with numerous small air discharge passages I3. Attention is directed to the fact that this novel matrix is of a shape and size to receive within its transverse cross-section substantially only the newly applied tread material, as shown in Figs. 6 and '7. The importance of the use of such a matrix,

when used in the novel manner hereinafter set forth, will become apparent.

The matrix may be heated in any desired manner but, preferably and as illustrated, this is accomplished by means of a steam coil I4 wound on the outer surface of the annular member 9, which member 9 is formed of quite light material and will be quickly and economically heated by said coil. This coil I4 may be connected to receive steam from any suitable source, not shown, through a delivery pipe interposed in which is a control valve. Obviously, the coil Il may be insulated against heat loss in any wellknown manner.

The tire casing illustrated is of the character generally used on motor vehicles of the present day and comprises the customary cord carcass I5 of cross sectionally normally round shape from bead to bead having reinforced bead portions I6, a breaker strip I1, a rubber covering forming a road engaging crown tread portion I8, shoulder tread portions I9, and side wall protecting portions 20. The tire illustrated has a normal outside circumference greater than that of the inside of the matrix. This is best illustrated by the dotted circle X in Fig. 4, which illustrates the "tire in a normally circumferentially expanded condition.

Fig. 2 illustrates a typical example of how an can most conveniently be ordinary casing appears after having been run until its road engaging crown tread portion II has been 'worn thin and smooth. It should here be noted that while the center of the crown tread is very thin, the shoulder tread portions I9 on either side thereof and the side walls are in very tread 2| to the worn crown of the tire substantially as shown in Fig. 3. This new tread is preferably in the form of unvulcanized rubber strip of slightly less width than the distance between the matrix retaining ribs I0, see particularly Fig. 5. The new tread rubber 2| may be applied in any suitable manner but is preferably cemented on the worn crown.

The next step in the method is to enter the casing into the matrix, which matrix has an inside circumference less than normal outside circumference of the casing. This is accomplished by laterally spreading the bead portions I6 of the casing and thereby circulnferentially contracting the tread portion thereof to a less circumference than that of the inside of the matrix, and then placing the circumferentially contracted casing within the matrix as shown by'full lines in Figs. 4 and 5.

Any suitable means for spreading the bead portions of the casing may be provided but as illustrated I provide spreading devices 22 applied at circumferentially spaced points. These spreading devices 22 each comprise a screw 23 having a hand-piece 24 at one end thereof, a head engaging lug 25 swiveled to the other end thereof and a nut-acting head engaging lug 26 on the screw 23 intermediate the handle 24 and lug 25.

The next step in the method consists in releasing the casing from lateral spreading action, by removing the spreading devices 22, and thereby permitting the casing to expand circumferentially and bring its newly applied tread 2| into contact with the matrix tread-forming ribs II. Because the matrix has an inside circumference less than the casing being treaded therein, it will be obvious that even after the casing has come into contact with the matrix it will be in a radially deformed condition, see Fig. 6, and the inherent resiliency of the deformed casing will cause it to exert an outward expanding force against the matrix as it tends to return shown in Fig. 2.

The next step consists in applying expanding pressure to the crown and shoulder portions of the casing to thereby further press the newly ap plied crown tread tightly against the forming ribs II and the road engaging surfaces of the original shoulder tread portions, at each side of the newly applied tread and tightly against the confining ribs III, as shown in Fig. 6. Thi circumferential expanding action is preferably and produced by placing the customary inner tube Tim the casing, mounting the customary rim 28 and inflating the tire by applying fluid' pressure within the tube in the ordinary manner. In order to insure positive contact between the shoulders and confining ribs II! it is advisable to hold the casing against lateral expansion, under the action of fluid pressure, thereby increasing the circumferential expanding action of the shoulder portions thereof to its normal shape and for this purpose I provide a pair of annular members or rings 28a, which rings are applied in opposed relation one to each side wall of the casing, and suitable clampings 29, only one of which is here illustrated, arranged to press the rings 28a toward one another. These clamps 29 each comprise a U-shaped body 30 and a clampi screw 3|.

cumferentially spaced points about the rings 28a.

. Fig. 6 illustrates the complete assembly as it appears at the completion of this last described step in the method and by reference to said figure it will be noted that the tread forming ribs I I have been partially pressed into the newly applied tread 2| and that the crown portion of the original casing tread is now held in a somewhat concave form. v

The next step in the method consists in forming and vulcanizing the new tread and to this end the matrix is heated by passing steam through the matrix heating coil I4. Under this heat and continued circumferential expanding pressure of the casing the forming ribs I I will completely enter the newly applied treadand the confining ribs III will enter the original shoulder tread portions of the casing substantially as illustrated in Fig. 7. During this step, of course, the newly applied tread will flow between the forming ribs II, through gates I2, and thereby equalize pressure thereon. Pressure being greatest near the shoulders of the casing, due to the fact that the sides of the casing are held against lateral expansion, will cause the newly applied tread to flow away from the edges of the crown toward the center thereof and equalize expanding pressure of the casing on the new crown tread and said tread will be Vulcanized in a substantially fiat condition, as indicated inFig. 7. The retaining ribs III positively confine the newly applied tread therebetween during the vulcanizing period and form continuous annular grooves 32 in the original shoulder tread portions I! of the casing and the forming ribs II form broken grooves 33 in the newly applied crown tread.

Attention is here called to the fact that the combined action of heat and pressure, while sufficient to cause the retaining ribs III to enter the original shoulder tread, it will not be suflicient to cause the edge portions of the matrix that.overlap the original shoulder tread to deface or alter the character of said shoulder tread. These edge portions of the matrix simply come to rest against the original shoulder tread and act as stops to limit entering movements of the retaining ribs I0 into the shoulder tread.

After the vulcanizing process has been completed, the tire may be deflated, the rings 28a, tube 21 and rim 2B removed from the casing and the casing removed from the matrix. To remove the casing from the matrix, it is again laterally expanded by means of the spreading devices 22 and thereby circumferentially contracted suiilciently to withdraw its tread from the matrix ribs I0 and II.

After removing the newly retreaded casing from the matrix and releasing the same from lateral spreading action, it will return to its normal shape and will appear substantially as illustrated in Fig. 8. This returning of the casing to its normal shape causes the newly applied crown tread, which was vulcanized in a cross-sectionally flat condition to round out and appear much like tread found on most new casings.

In practice it has been found that best results can be obtained from a retreaded casing if it is The clamps are applied at cir- Y permitted to cool under pressure in the matrix. This practice can very economically be followed when my apparatus is employed because, first the matrix is light and will cool so rapidly that it will not greatly retard the speed of successive retreading operations and second, because extra equipment can be provided without great added expense.

Also each of varying dimensions and, therefore, a less number of different size matrices are required than where mold equipment accommodating only one size tire is employed. The reason for this is that with my disclosed method and apparatus, contrary to the prior practices, the curing matrix does not receive any of the worn casing within its transverse cross section prior to the applicationcf vulcanizing pressure and heat and does not at any time during the method receive any of the cord carcass within its transverse crosssection. In other words the shoulder portions as well as the cord carcass during the fitting of the casing to an undersize matrix as well as during curing are left free for lateral expanding action so that the casing may be free to compensate by way of flattening and increased crosssectional width for the decreased circumferential length due to radial contraction and deformation.

This new concept of utilizing a matrix which does not, prior to application of vulcanizing pressure and heat, receive any of the worn casing within its transverse cross-section but leaves it free to expand laterally, is the factor which makes possible the use of an undersize matrix without fear of buckling, pinching, wrinkling or otherwise damaging the cord carcass-a result invariably experienced by. the use of a prior art mold of less circumference than the normal circumference of the casing.

Another way of stating this difference is that in my method the only pressure which is permitted between the deformed casing and the matrix is in a direction radial to the axis of the casing, whereas in the prior methods, a large portion of the tire casing cross-section being received within the matrix, pressures exerted by the tire against the mold or matrix were necessarily both radial and longitudinal to the easings axis. a

As illustrated diagrammatically in Fig. 9, tire casing carcasses are customarily made up of crossed cords 34 that extend from head to bead of the casing on a diagonal to the axis thereof and these crossed cords 3| are adhered together by suitable quite soft rubber which permits considerable movement of the cords in respect to one another. It is this arrangement of the cords that is responsible for the circumferential contraction of the casing under lateral expanding pressure. By reference to Fig. 9, it will be apparent that under lateral spreading pressure the angles of the cords 34, in respect to the axis of the casing, will be decreased with the result that the casing will actually stretch laterally and contract circumferentially. It is, of course, this action of the cords that gives flexibility to tire casings.

It should also be apparent that by the practicing of the above method not only is the tread element applied to the worn casing, of smaller circumference than the normal circumference of the tire casing, but also that the crown portion of the cord carcass, as well as the road engaging surface of the newly applied tread material,

size matrix will accommodate casings I are radially deformed and flattened throughout their circumference.

Attention is here called to the fact that treads applied to casings, which are in a circumferentially contracted cross-sectionally flattened condition, will stretch and be maintained under tension when the casing is returned to a normal condition, and that this tendency of the tread to return to a cross-sectionally flattened, circumferentially contracted condition renders the easing more easily flexed as it rolls over a road and therefore reduces road resistance to a minimum.

From the foregoing it will be obvious that while the invention is particularly described for use in treading casings having worn-off or otherwise reduced crown tread portions, it will be readily appreciated by those skilled in the art that the method and apparatus is equally adapted without modification, for the application of tread material to the crown portion of tires having less than the desired thickness or formation of tread.

What I claim is: w,

1. The method of treading tire casings, which comprises spreading the side walls of the casing laterally at circumferentially spaced points to circumferentially contract the crown portion of the casing, then placing the circumferentially contracted casing within a matrix having an inside circumference less than that of the normal circumference of the casing, permitting expansion of the casing against the matrix by relieving the same from lateral spreading action, applying circumferential expanding pressure to the casing to expand the same under pressure against the matrix, and applying heat to the matrix.

2. The method of treading tire casings, which comprises applying tread material to the crown of the casing, in laterally spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing, in placing the circumferentially con tracted casing within a surrounding matrix having an internal diameter less than the normal diameter of the casing, in circumferentially expanding the casing against the surrounding matrix, and in applying heat to the matrixrto cure the applied crown tread material on to the crown of the casing.

3. The method of treading tire casings, which comprises applying tread material to the crown of the casing, in laterally spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing, in placing the circumferentially contracted casing with its applied tread material within a surrounding matrix having an internal diameter less than the normal diameter of the treaded casing, in circumferentially expanding the casing against the surrounding matrix to bring the shoulders of the casing into sealing contact with the opposite side portions of the cylindrical mold, whereby to confine the tread material therebetween, and applying heat to the matrix to cure the confined crown tread material to the crown of the casing.

4. The method of treading tire casings, which comprises applying tread material to the crown of the casing, in laterally spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing, in placing the circumferentially contracted casing with its applied tread material within a surrounding matrix having an internal diameter less than the normal diameter of the treaded casing, in circumferentially expanding the casing against the surrounding matrix to bring the shoulders of the casing into sealing contact with the opposite side portions of the cylindrical mold, whereby to confine the tread 5 material therebetween, and applying heat to the matrix to cure the confined crown tread material to the crown of the casing, cooling the cured tread while under such expanded condition within the matrix, in relieving the casing from circumferential expanding pressure and thereafter laterally spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing to free the tire from the surrounding matrix.

5. The method of treading tire casings, which comprises applying tread material to the crown of the casing, in laterally spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing, in placing the circumferentially contracted casing with its applied tread material within a surrounding matrix having an internal circumference less than the normal circumference of the casing,in permitting expansion of the casing by relieving the same from lateral spreading action, in forcing the casing against the matrix by applying expanding pressure within the same while holding the side walls of the casing against spreading action, but leaving the shoulder portions of the casing outward of the matrix free for radial expanding action.

6. The method of treading tire casings having moldable tread material at the crown of the casing and intermediate the shoulders thereof, in placing the casing within and expanding the a crown portion to compress the moldable tread )5 portion against an annular matrix, applying heat :i' to the matrix to mold and cure the tread mate-1M rial, and finally removing the casing from within the matrix by laterally spreading the side walls, of the casing at circumferentially spaced points 316 circumferentially contract the crown portion thereof out of engagement with the mold.

7. The method of applying a new road engaging tread element to a worn tire casing having a cord carcass which is cross-sectionally normally round from bead to bead and an external rubber covering constituting in part a worn road engaging crown tread and laterally spaced relatively thick shoulder tread portions, which method consists in applying a circular band of new tread material to the worn crown tread surface intermediate said shoulders, in radially deforming said casing throughout its circumference and in per- 5 mitting expansion of said radially deformed casing against an annular matrix of less circumierence than that of the normal circumference of the casing and which matrix engages only the nowly applied crown tread and adjacent road engaging surfaces of the shoulder portions so as not w to receive any of the worn casing within its transverse cross-section prior to the application of vulcanizing pressure and heat, in applying internal expanding pressure to the casing and applying 6- heat to the matrix.

8. The method of applying a new road engaging tread element to a worn tire casing having a cord carcass which is cross-sectionally normally round from head to bead and an external rubber covering constituting in part a worn road-em gaging crown tread and laterally spaced relatively thick shoulder tread portions, which method consists in applying a circular band of new tread material to the worn crown tread surface intermediate the cross-sectionally outer parts of said shoulder portions, and in radially deforming said casing throughout its circumference and in permitting expansion of said radially deformed casing against an annular matrix of less circum ference than that of the normal circumference of the casing and which matrix contacts the worn casing only on the thick shoulder portions and does not receive any of the cord carcass within its transverse cross-section, in applying internal expanding pressure to the casing and applying heat to the matrix.

9. The method of applying a new road engaging tread element to a pneumatic tire casing having a cord carcass which is cross-sectionally normally round from head to bead and a rubber covering, which consists in applying an annular band of uncured tread rubber to the road engaging crown surface of the rubber covering, in deforming the casing throughout its circumference by radially contracting the crown portion thereof, and in curing said newly applied rubber to the casing in an annular matrix which, prior to the application of vulcanizing pressure and heat, does not receive within its transverse crosssection any of the worn casing, and in holding the crown portion of the cord carcass and the road engaging surface of the new tread material in a radially deformed cross-sectionally substantially flat position during the curing operation.

10. The method of applying a road engaging tread element to a pneumatic tire casing having a cord carcass which is cross-sectionally normally round from head to head and a rubber covering, which consists in applying.a strip of uncured tread rubber to the rubber covering, in deforming the casing throughout its circumference so that the crown portion of the cord carcass and the road engaging surface of the new tread material are in a cross-sectionally substantially flat condition, and in curing said newly applied rubber to the casing while holding the new rubber and the cord carcass so deformed in an annular matrix which does not receive within its transverse cross-section any of the cord carcass.

11. The method of applying a road engaging tread element to a pneumatic tire casing having a cord carcass which is cross-sectionally normally round from bead to bead and a rubber covering, which consists in applying a strip of uncured tread rubber to the rubber covering, in radially deforming the casing throughout its circumference within an undersize annular matrix which during said operation does not receive any of the worn casing within its transverse cross-section, and in curing the newly applied tread material to the rubber covering while the crown of the cord carcass and the road engaging surface of the new rubber are held in a cross-sectionally substantially flat position within the matrix.

12. The method of treading tire casings which comprises applying tread material to the crown of the casing and laterally-spreading the side walls of the casing at circumferentially spaced points to circumferentially contract the crown portion of the casing, in placing the circumferentially contracted casing within a surrounding matrix having an internal diameter less than the normal diameterof the casing and which matrix does not receive within its transverse cross-section any of the tire casing during said operation, in circumferentially expanding the casing against the surrounding matrix and in applying heat to the matrix to cure the applied crown tread material onto the crown of the casing.

arose and subjacent cord carcass portions of the casing within an annular vulcanizing matrix of a size and shape to engage only the newly applied tread material and shoulder portions immediately adj acent thereto, supporting said crown tread and subjacent cord carcass portions in said radially deformed condition without embracing any of said carcass within the transverse cross-section of said matrix prior to the application of heat, whereby said deformed casing is permitted to exert its expansive force against the matrix only in a direction radial to the axis of said casing, thereafter exerting internal radial pressure against the deformed casing to compress the applied strip against the matrix, and applying heat to the matrix to vulcanize said compressed strip to the casing while said casing is supported in said deformed condition within the matrix.

PAUL E. HAWKINSON. 

